DocID023775 Rev 1

11/16

TN0941

What are the following additional options of reset and supervisor ICs used for?

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6.4

Chip enable gating

Internal gating of the memory chip enable signal (E) prevents erroneous data from

corrupting the external SRAM in the event of an undervoltage condition. The chip enable

signal, which normally goes directly from the microcontroller to the SRAM, is routed instead

through the supervisor device. The short propagation delay enables the chip enable gating

to be used with most microcontrollers. During normal operation (reset not asserted), the

transmission gate is enabled and passes all E transitions. When reset is asserted, this path

becomes disabled, preventing erroneous data from corrupting the SRAM.

More details

See AN1957: Microprocessor Supervisor Functions, page 17

Suggested products

For further information on chip enable gating signals, please refer to STM795 and STM818.

6.5

Early power failure

Inadvertent or unexpected power loss can cause a number of malfunctions in a system

(example, data loss, uncontrolled program status, and indeterminate processor state). For a

reliable design, systems should receive early power failure warnings, to leave enough time

for the microprocessor to start a safeguard routine, for backing up crucial data (example,

registers). Hence, power fail comparators are used to monitor unregulated or failing power

supplies through a voltage divider. Their reaction to power loss is very fast, and can provide

enough time to execute all the necessary safeguard processes that precede an expected

power failure.

More details

•

See AN1957: Microprocessor Supervisor Functions, page 18

•

See AN1336: Power-Fail Comparator for NVRAM Supervisory Devices

Suggested products

For further information on early power failures, please refer to the following products

STM69x, STM70x, STM80x, STM81x, and STM1404.

Design tip

The power fail comparator input may be connected to a manual reset so that an early low

voltage condition generates a reset output.